[CH2:1]([N:8]1[CH2:13][CH2:12][CH:11]([C:14]([O:16]C)=O)[CH:10]([C:18]2[CH:23]=[C:22]([CH3:24])[CH:21]=[C:20]([Br:25])[CH:19]=2)[CH2:9]1)[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.[NH4+].[Cl-]>O>[CH2:1]([N:8]1[CH2:9][C@H:10]2[C@H:11]([C:14](=[O:16])[C:23]3[C:18]2=[CH:19][C:20]([Br:25])=[CH:21][C:22]=3[CH3:24])[CH2:12][CH2:13]1)[C:2]1[CH:3]=[CH:4][CH:5]=[CH:6][CH:7]=1A mixture of methyl 1-benzyl-3-(3-bromo-5-methyl-phenyl)piperidine-4-carboxylate (12.2 g, 30.3 mmol) from step B and polyphosphoric acid (124 g) was heated at 180° C. for 3 h then cooled to 0.20° C. To the reaction mixture H2O and saturated NH4Cl aqueous solution were added, successively then extracted with EtOAc. The combined organic solution was dried over MgSO4, filtered and concentrated in vacuo. The residue was chromatographed in silica gel column (Hex/EtOAc 9/1) to obtain the title compound (760 mg, 2.1 mmol): MS (ES) 370.1 (M+H).
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